1. Field of the Invention
This invention relates generally to a device for selectively holding and releasing reefing lines on parachute canopies or the like, and more particularly to a timer setting mechanism for such dereefing devices.
2. Description of the Related Art
The use of parachutes, either for air dropping heavy payloads or decelerating high-speed aircraft, requires the incorporation of suitable means to regulate the opening of the various parachute canopies. If not regulated, deceleration of the payload caused by rapid parachute canopy opening may be excessive, imposing potentially destructive forces on the attached payload. Additionally, for payloads delivered using multiple parachutes, the opening of each parachute must be controlled so that no single parachute interferes with, or “starves”, the opening of the remaining parachutes.
To control the opening rate of each parachute canopy, so-called reefing lines are employed, typically encircling the rim of the parachute canopy. The reefing lines are held by a dereefing device and the reefing line is sized so that the parachute canopy cannot fully open as long as the reefing line ends are held by the dereefing device. The dereefing devices are associated with timers or barometrically controlled devices, which after a given time or at a given altitude release the reefing line ends, enabling full opening of the associated parachute canopy. Multiple, differently sized reefing lines may be used for each parachute canopy, with each reefing line released sequentially so that the canopy can be opened in controlled stages, allowing further control over payload deceleration.
Dereefing devices can generally be classified into either destructive or nondestructive types. The destructive types include those using explosive charges or mechanically actuated blades to sever the reefing line. Destructive dereefing devices do not allow reuse of the reefing line and/or the dereefing devices themselves. Nondestructive reefing devices typically capture a reefing line end loop around a pin. The pin is releasably held within a yoke. The pin is withdrawn from the yoke to release the dereefing line end loops.
Some nondestructive dereefing devices utilize mechanical timers to determine the release point for the mechanical dereefer. There is a need in the art for a timer-setting mechanism which ensures accurate and repeatable timer setting and actuation.